7-(3-t-Butoxycarbonylamino-4-methyl-1-pyrrolidinyl)-8-chloro-1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-3-quinolinecarboxylic acid → 7-(3-Amino-4-methyl-1-pyrrolidinyl)-8-chloro-1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-3-quinolinecarboxylic acid

7-(3-t-Butoxycarbonylamino-4-methyl-1-pyrrolidinyl)-8-chloro-1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-3-quinolinecarboxylic acid (0.35 g) was dissolved in the mixture of methanol (5 ml) and concentrated hydrochloric acid (5 ml) and stirred at room temperature for 30 minutes. After the reacting mixture was concentrated under reduced pressure, the resulting residue was dissolved in ethanol (10 ml) and neutralized with concentrated aqueous ammonia. The resulting precipitate was collected by filtration, washed with water and recrystallized from chloroformmethanol-concentrated aqueous ammonia to give the title compound (0.07 g) as pale yellow powder, mp 231°-234° C.